Digital Ionograms Now Retrievable

Volume 13, Number 1, March 1997By Dieter Bilitza

NSSDC is now receiving digital International Satellite for Ionosphere Studies (ISIS) ionograms on a regular basis and is making them available for retrieval through its NASA Data Archive and Distribution Service (NDADS)/Space Physics Catalog (SPyCAT) system http://nssdc.gsfc.nasa.gov/space/ndads/spycat.html. Included are the full resolution ionograms (8-bit receiver-amplitude values collected at a 40 kHz rate) and the averaged ionograms (averages of each four successive 40 kHz 8-bit values). At NSSDC the average ionograms are converted from their original binary format to Common Data Format (CDF) and are being made available for retrieval, in binary or CDF, through the NDADS/SPyCAT and for viewing through NSSDC/Space Physics Data Facility's CDAWeb graphics system at http://cdaweb.gsfc.nasa.gov/cdaweb/sp_test/. First time users of the CDAWeb/ISIS system are encouraged to consult http://nssdc.gsfc.nasa.gov/space/isis/cdaweb_comments.html.

The ionograms are the result of a data restoration effort headed by Robert Benson of Goddard's Laboratory for Extraterrestrial Physics. His team is converting ISIS 2 topside sounder ionograms from the original analog telemetry tapes to a digital format. The plan is to perform a similar conversion for ISIS 1 and Alouette 2 ionograms. The Alouette and ISIS topside sounders have produced the only global mapping of the topside ionosphere over more than an entire solar cycle. Some of these ionogram data have been captured on 35-mm film (NSSDC has more than 12,000 rolls), and a small percentage has been converted to electron density profiles and is stored at NSSDC on magnetic tapes.

The ISIS data rescue project, supported by the NASA Space Physics Data System, has selected some 13,800 telemetry tapes for A/D conversion and has shipped them from Canada to Goddard Space Flight Center. Some 4,000 additional tapes have been set aside in Canada for possible future A/D conversion. All other Alouette/ISIS telemetry tapes have now been destroyed because of problems with media deterioration and the cost of tape storage. The tapes shipped to Goddard were selected so as to obtain global coverage and to accommodate community requests to address subjects and time periods of special interest.

More information about the background of this project and about the A/D conversion software and hardware can be found at http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html. The Web pages also provide a current listing of the available data and a description of the tape selection process and criteria.